The present invention relates to systems for water monitoring and sampling, more particularly, to multi-level monitoring wells. A major objective of the present invention is to provide for enhanced determination of vertical gradients in pressure and water quality in groundwater.
Contamination of water is a major environmental concern. Toxic compounds can remain in groundwater, causing serious environmental and health problems, and can seep into surrounding soils. Quick, accurate evaluation of the contamination is critical, especially where there is a threat to health. Because contamination often spreads deep below the surface, and because there are variations in the vertical migration patterns of contaminants, identifying and treating contaminated water and soil can be problematic.
The extent and nature of a contaminant spill can be difficult to determine. The rapidity and nature of spread can be unpredictable, depending on the chemical composition and physical or biological properties of the contaminant, on water and soil conditions, on the weather, and on the characteristics of the soil and geologic formations. For example, consider a chemical spill or leak of multiple chemical components. Each may have a different solubility, and portions of the spill may encounter different water and soil conditions, causing them to spread different.
One approach to testing soil or water involves drilling or boring multiple holes at various locations and to various depths. Samples are then taken from the boreholes or instruments lowered in, and the results are analyzed to assemble an overall picture of the contamination. However, because of significant viability in dispersal of contaminants, the picture can be wrong or misleading. Also, this approach requires a lot of drilling, which takes time. Finally taking samples at just one depth in each hole is unsuitable for accurate assessments of vertical gradients, which requires monitoring at multiple levels within a single hole.
Unfortunately, sampling from multiple levels in the same hole has its own problems. Multi-level monitoring procedures can unintentionally alter the contaminant profiles they are trying to observe. In any system that involves placing equipment in a hole or well new drilling, the sampling equipment itself or water flow in the well can spread the contaminants, leading to inaccurate measurements. The borehole can crumble or erode, carrying contaminants between levels. To mitigate this, the annulus between the borehole and introduced equipment can be sealed off by backfiring or by the use of expandable packers (typically inflatable) that seal the hole at specified intervals to isolate the different sampling intervals.
One approach using es to seal off borehole intervals is described in U.S. Pat. No. 5,195,583 to Toon et al, “Toon” hereinafter. In Toon, packers include bentonite, which expands upon contact with groundwater naturally occurring in the borehole. However, this system can provide less than ideal results. If the borehole contains insufficient groundwater to expand the packer fully, the annulus will not be sealed, and the sampling intervals will not be isolated from each other. Also, the bentonite near the entrance port tends to become saturated and impermeable before the water can reach more distant bentonite, causing insufficient packer expansion. To counteract this tendency, the system of Toon includes means such as distributed blotting paper and very small plastic pipes to effect the even penetration of groundwater. Because these measures require specially placed water distribution means, they add to the time and expense of producing the packers. Furthermore, the distribution means are subject to displacement by jostling or installer error, which decreases the reliability of the system.
In another approach, a relatively large diameter hole is drilled, and pipes cut to different lengths are inserted into the hole. The insertion of separate pipes involves a costly repetition of several steps. Bundling tubes eliminates the need for repetitive insertion, but is also problematic. The bundled tubes must be carefully threaded into each section of casing, which is very time-consuming. Furthermore, individual tubes in a bundle often move relative to each other, complicating installation. Bundled tubes also permit fluid flow between the tubes, making it difficult to seal the well between intervals.
In another approach, described in U.S. Pat. No. 4,838,079 to Harris, pipe sections include interior elements that divide the sections into chambers. When the sections are joined, a sectioned pipe with longitudinal chambers is created. However, because the system of Harris is jointed, the sectioned pipe is vulnerable to leaking if strained or jarred. Furthermore, the reinforced joints can decrease the flexibility of the system complicating installation.
What is needed is a convenient, cost-effective apparatus and method for testing groundwater or other fluids at multiple depths with minimal perturbation of the sample distribution being measured.